When physical energy has resulted in a response in a sense organ, it is clear that:

1. Perception has taken place
2. the activation is the result of stimulus
3. the brain has interpreted the event.
4. a single isolated sense is now perceiving the event.

The correct answer is 2. The activation is the result of stimulus.

When physical energy causes a response in a sense organ, it indicates that a stimulus has occurred. This stimulus triggers the activation of the sense organ, which then sends signals to the brain for further processing. So, the response in the sense organ is a result of the stimulus, indicating that the physical energy has caused a reaction in the sense organ.

Perception (choice 1) refers to the process by which we interpret and make meaning out of sensory information. It involves not only the initial response in the sense organ but also the subsequent processing and interpretation in the brain. Therefore, it cannot be concluded solely based on the fact that physical energy triggered a response in a sense organ.

The interpretation by the brain (choice 3) is indeed an important part of perception, but it goes beyond the immediate response in the sense organ. It involves the overall processing and integration of sensory information in the brain.

Choice 4 is incorrect because the statement refers to a single sense perceiving the event, whereas in reality, our perception is often a combination of inputs from multiple senses.